rzsionak

I just picked up a used tandem and my son is about 1” too short with seat all the way down. I think there are two options:
1. Switch out the suspension seatpost with a regular seatpost to lower the seat further.
2. Put on crank shorteners

A third option would be a thinner saddle, though I don’t think I’ll get the inch I want from it.

Any advise or experience would be appreciated.

Joint Venture

Maybe both #1 and #2 together. If the cranks are too long, that’s a separate problem from whether the saddle is too high or not. FYI, da Vinci makes short cranks as well as some 3-hole cranks too (good for when both a child and an adult will be a stoker on the same tandem - just move the pedals!).

OneIsAllYouNeed

I agree with Joint Venture's recommendation to do both. Lower profile seatpost AND shorter cranks. The cranks should be about the same length as your son's single bike. My 5yo daughter's 14" bike has 102mm cranks, so that's the shortest crank length on our kiddie stoker setup.
Also note that little kids are light. You should lower the rear tire pressure to give them some suspension.


Kid stoker setup with telescoping seat post and multi-hole crankarms.

WheelsNT

If you get a straight post with a separate clamp like on inexpensive bikes, you can flip the clamp over so the clamp bolt and nuts are above the saddle rails. This will get the rails to around the top of the frame clamp. I agree with others that you probably need to do crank shorteners as well.

rzsionak

I ended up doing both, and that probably was the best choice for fitting my son and for flexibility in the future.